1. Field
Aspects of the present disclosure relate to polymer compositions, cross-linked polymers formed therefrom, electrodes and electrolyte membranes for a fuel cell including the cross-linked polymers, and fuel cells including the electrodes and the electrolyte membranes.
2. Description of the Related Art
Fuel cells that include a polymer electrolyte membrane operate at relatively low temperatures and may be manufactured in small size. Thus, such fuel cells are expected to be used as energy sources in electric vehicles and in distributed generation systems. Perfluorocarbon sulfonic acid-based polymer membranes, such as NAFION membranes (registered trade mark), are commonly used as polymer electrolyte membranes for fuel cells.
However, such polymer electrolyte membranes should be humidified, in order to sufficiently conduct protons. In addition, to enhance cell system efficiencies, polymer electrolyte membranes should be operated at high temperatures, i.e., 100° C. or more. However, the moisture in the polymer electrolyte membrane is evaporated and depleted at such temperatures, which reduces the effectiveness thereof.
To address such problems and/or other problems in the related art, non-humidified electrolyte membranes, which may operate at temperatures of 100° C. or more, without humidification, have been developed. For example, polybenzimidazole doped with phosphoric acid is disclosed as a material for a non-humidified electrolyte membrane.
In addition, phosphoric acid fuel cells, which operate at temperatures of from 150 to 200° C., include a liquid phosphoric acid electrolyte. However, the liquid phosphoric acid included in a large amount in electrodes interferes with gas diffusion in the electrodes. Therefore, an electrode catalyst layer that includes a polytetrafluoroethylene (PTFE) waterproofing agent, which prevents fine pores in the electrodes from being clogged by the phosphoric acid, has been used.
In fuel cells employing a phosphoric acid-impregnated polybenzimidazole (PBI) electrolyte membrane as a high-temperature, non-humidified electrolyte, in order to promote contact between an electrode and an electrolyte membrane, attempts have been made to impregnate an electrode with liquid phosphoric acid and to load a larger quantity of a metal catalyst. However, the mechanical characteristics, chemical stability and phosphoric acid-retaining capability of such fuel cells may not be satisfactory, and thus, there is still a demand for improvement.